Lipopolysaccharide (LPS) is a common component of gram negative bacteria cell walls which acts as a potent inducer of cytokine release from human monocytes. The purpose of this project is to isolate and identify the protein(s) on human monocytes which bind LPS and initiate the release of cytokines from these cells. Using sepharose beads which have been covalently crosslinked with LPS, we have isolated two proteins from human monocytes lysates, which appear to bind specifically to the LPS coated beads and not the control beads. The molecular weight of these proteins are approximately 73 and 85 kd. The 73 kd protein appears to be present in greater abundance. Two other groups, using different techniques, have likewise isolated a protein of approximately 73 kd which appears to bind LPS. Currently, using Western blot analysis, we have tentatively identified this protein. Studies are underway to confirm this identification and to determine whether this molecule plays a significant role in transducing the necessary signals to induce cytokine release from human monocytes.